Battery pack enclosure with controlled thermal runaway release system

ABSTRACT

A battery pack thermal management system is provided that is comprised of at least one enclosure failure port integrated into at least one wall of a battery pack enclosure, where the enclosure failure port(s) remains closed during normal operation of the battery pack, and opens during a battery pack thermal runaway event, thereby providing a flow path for hot gas generated during the thermal runaway event to be exhausted out of the battery pack enclosure in a controlled fashion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 12/798,198, filed 30 Mar. 2010, now U.S. Pat. No. 8,277,965, whichis a continuation-in-part of U.S. patent application Ser. No.12/386,684, filed Apr. 22, 2009, the disclosures of which areincorporated herein by reference for any and all purposes.

FIELD OF THE INVENTION

The present invention relates generally to battery packs and, moreparticularly, to a system for controlling the release of thermal energyand hot gas from a battery pack undergoing thermal runaway.

BACKGROUND OF THE INVENTION

There is currently a trend in the automotive industry to replacecombustion engines with electric motors or a combination of an electricmotor and a combustion engine, thereby substantially reducing theenvironmental impact of automobiles by reducing (i.e., hybrids) orcompletely eliminating (i.e., electric vehicles) car emissions. Thisswitch in drive train technology is not, however, without itstechnological hurdles as the use of an electric motor translates to theneed for inexpensive batteries with high energy densities, longoperating lifetimes, and operable in a wide range of conditions.Additionally, it is imperative that the battery pack of a vehicle poseno undue health threats, either during vehicle use or during periods ofstorage.

While current rechargeable battery technology is able to meet thedemands of the automotive industry, the relatively unstable nature ofthe chemistries used in such batteries often leads to specializedhandling and operating requirements. For example, rechargeable batteriessuch as lithium-ion cells tend to be more prone to thermal runaway thanprimary cells, thermal runaway occurring when the internal reaction rateincreases to the point that more heat is being generated than can bewithdrawn, leading to a further increase in both reaction rate and heatgeneration. Eventually the amount of generated heat is great enough tolead to the combustion of the battery as well as materials in proximityto the battery. Thermal runaway may be initiated by a short circuitwithin the cell, improper cell use, physical abuse, manufacturingdefects, or exposure of the cell to extreme external temperatures. Inthe case of a battery pack used in an electric vehicle, a severe carcrash may simultaneously send multiple cells within the battery packinto thermal runaway.

During a thermal runaway event, a large amount of thermal energy israpidly released, heating the entire cell up to a temperature of 850° C.or more. Due to the increased temperature of the cell undergoing thermalrunaway, the temperature of adjacent cells within the battery pack willalso increase. If the temperature of these adjacent cells is allowed toincrease unimpeded, they may also enter into a state of thermal runaway,leading to a cascading effect where the initiation of thermal runawaywithin a single cell propagates throughout the entire battery pack. As aresult, power from the battery pack is interrupted and the systememploying the battery pack is more likely to incur extensive collateraldamage due to the scale of thermal runaway and the associated release ofthermal energy.

A number of approaches have been employed to either reduce the risk ofthermal runaway, or reduce the risk of thermal runaway propagation. Forexample, by insulating the battery terminals and using specificallydesigned battery storage containers, the risk of shorting during storageand/or handling can be reduced. Another approach is to develop new cellchemistries and/or modify existing cell chemistries. Yet anotherapproach, disclosed in co-pending U.S. patent application Ser. Nos.12/504,712, 12/460,372, 12/460,342, 12/460,423 and 12/460,346, is toprovide additional shielding at the cell level, thus inhibiting the flowof thermal energy from the cell undergoing thermal runaway to adjacentcells. Still yet another approach, disclosed in co-pending U.S. patentapplication Ser. No. 12/545,146, is to use a spacer assembly to maintainthe position of the battery undergoing thermal runaway in itspredetermined location within the battery pack, thereby helping tominimize the thermal effects on adjacent cells.

While a number of approaches have been adopted to try to lower the riskof thermal runaway as well as its propagation throughout the batterypack, it is critical that if a pack-level thermal runaway event doesoccur, personal and property risks are minimized. Accordingly, what isneeded is a system that controls the flow of the thermal energy and hotgas created during a cascading thermal runaway event. The presentinvention provides such a system.

SUMMARY OF THE INVENTION

A battery pack thermal management system is provided that is comprisedof an enclosure failure port assembly integrated into a wall of abattery pack enclosure, where the enclosure failure port assemblyremains closed during normal operation of the battery pack, and opensduring a battery pack thermal runaway event, thereby providing a flowpath for hot gas generated during the thermal runaway event to beexhausted out of the battery pack enclosure. The failure port assemblyis comprised of a region of the enclosure wall that is thinner than thesurrounding wall, where a portion of the perimeter of the region isthicker than a second portion of the perimeter so that the secondportion will fail before the first portion. The battery pack enclosuremay be comprised of a material with a melting temperature greater than800° C.; comprised of a material with a melting temperature greater than1000° C.; comprised of a material that includes an outer layer and aninner ceramic layer, for example where the inner ceramic layer preventsthe outer layer from melting during the battery pack thermal runawayevent; and/or comprised of a material that includes an outer layer andan inner intumescent layer, for example where the inner intumescentlayer prevents the outer layer from melting during the battery packthermal runaway event. Further, the battery pack enclosure may becomprised of first and second housing members with means to secure thetwo housing members together; and comprised of first and second housingmembers with means to secure the two housing members together and with asealing gasket configured to be interposed between the sealing surfacesof the first and second housing members. In at least one configuration,the system also includes a heat resistant channel, such as an open orclosed channel, that directs the flow of hot gas exhausted through theenclosure failure port during a thermal runaway event, for exampledirecting the flow away from a vehicle passenger compartment. In atleast one configuration, the system also includes at least one layer ofa thermal insulator positioned between the battery pack enclosure and avehicle passenger compartment. In at least one configuration, the systemalso includes at least one layer of a fire retardant material (e.g., anintumescent material) positioned between the battery pack enclosure anda vehicle passenger compartment.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a side view of a battery pack mounted under a car;

FIG. 2 provides a bottom view of the battery pack of FIG. 1;

FIG. 3 is a perspective view of a preferred embodiment of a battery packenclosure;

FIG. 4 is a perspective view of a preferred embodiment of a battery packenclosure utilizing a multi-section enclosure gasket;

FIG. 5 is a side view of a portion of a battery pack enclosureillustrating an embodiment of an enclosure failure mechanism;

FIG. 6 is a cross-sectional view of the enclosure failure mechanismshown in FIG. 5;

FIG. 7 is a cross-sectional view of an alternate enclosure failuremechanism using a thinned enclosure wall;

FIG. 8 is a cross-sectional view of an alternate enclosure failuremechanism using a scored enclosure wall;

FIG. 9 is a side view of a portion of a battery pack enclosureillustrating an alternate embodiment of an enclosure failure mechanism;

FIG. 10 is a cross-sectional view of the enclosure failure mechanismshown in FIG. 9;

FIG. 11 is a side view of a portion of a battery pack enclosureillustrating an alternate embodiment of an enclosure failure mechanism;

FIG. 12 is a cross-sectional view of the enclosure failure mechanismshown in FIG. 11;

FIG. 13 illustrates a modification of the embodiment illustrated in FIG.5, the modification directing the flow of hot gas and material out ofthe exhaust port;

FIG. 14 is a cross-sectional view of the enclosure failure mechanismshown in FIG. 13;

FIG. 15 illustrates a modification of the embodiment illustrated in FIG.7, the modification directing the flow of hot gas and material out ofthe exhaust port;

FIG. 16 illustrates an alternate view of the embodiment shown in FIG.15;

FIG. 17 illustrates an embodiment of the invention utilizing one or moreheat resistant channels to direct the flow from the battery packenclosure failure ports;

FIG. 18 is a cross-sectional view of an open channel for use with theembodiment illustrated in FIG. 17;

FIG. 19 is a cross-sectional view of a closed channel for use with theembodiment illustrated in FIG. 17;

FIG. 20 illustrates an embodiment utilizing thermal insulation to reducethe flow of thermal energy from the battery pack enclosure to adjacentvehicle regions; and

FIG. 21 illustrates an embodiment utilizing a blower fan to force airaround the battery pack enclosure.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the following text, the terms “battery”, “cell”, and “battery cell”may be used interchangeably and may refer to any of a variety ofdifferent rechargeable cell chemistries and configurations including,but not limited to, lithium-ion (e.g., lithium iron phosphate, lithiumcobalt oxide, other lithium metal oxides, etc.), lithium-ion polymer,nickel metal hydride, nickel cadmium, nickel hydrogen, nickel zinc,silver zinc, or other battery type/configuration. The term “batterypack” as used herein refers to multiple individual batteries containedwithin a single piece or multi-piece housing, the individual batterieselectrically interconnected to achieve the desired voltage and capacityfor a particular application. The term “electric vehicle” as used hereinrefers to either an all electric vehicle, also referred to as an EV,plug-in hybrid vehicles, also referred to as a PHEV, or a hybrid vehicle(HEV), a hybrid vehicle utilizing multiple propulsion sources one ofwhich is an electric drive system. It should be understood thatidentical element symbols used on multiple figures refer to the samecomponent, or components of equal functionality. Additionally, theaccompanying figures are only meant to illustrate, not limit, the scopeof the invention and should not be considered to be to scale.

The rechargeable batteries used in an electric vehicle (e.g., EV, PHEV,HEV) store a significant amount of energy. The amount of energy per celland the total amount of energy stored per battery pack depends upon thetype of cell and the number of cells within the pack. For example,lithium-ion cells with an 18650 form factor store approximately 30 kJ ofthermal energy when completely charged, and therefore a battery packwith 8000 cells stores up to approximately 240 MJ of thermal energy,depending upon the state of charge of the individual cells within thepack. When a cell within such a battery pack undergoes thermal runaway,it releases its thermal energy, some of which is in the form of hot gas(e.g., approximately 5 liters of hot gas for a lithium-ion 18650 cell).These jets of hot gas, in combination with the heat generated duringsuch an event, may cause adjacent cells to enter into thermal runaway.Therefore if the initial thermal runaway event is not effectivelymanaged, more and more cells will enter into thermal runaway untileventually all of the cells within the battery pack may be consumed.

While it is clearly desirable to quickly detect a cell undergoing thefirst stages of thermal runaway and then manage the event before it canpropagate throughout the battery pack, preferably precautions are alsotaken to limit the risk to the vehicle's passengers and, to the extentpossible, limit collateral property damage in the case that the event isnot quickly extinguished. Such precautions are especially importantgiven the amount of thermal energy, hot gas, and smoke that may bereleased if the event propagates throughout the battery pack. Thepurpose of the present invention is the control of the thermal energy,hot gas and smoke released during such an event.

FIGS. 1 and 2 provide side and bottom views, respectively, of a car 100with a battery pack 101 mounted underneath the car. It should beunderstood that the battery pack configuration shown in FIGS. 1 and 2 issimply for illustration purposes and that the invention is equallyapplicable to other configurations. In general, the location of thebattery pack is based on a number of design criteria including, but notlimited to, battery pack size and weight to achieve the desiredperformance, cell choice, distribution of the battery pack weight toachieve the desired vehicle performance, constraints due to vehiclesize, location of vehicle undercarriage support frame members, passengercompartment size and configuration (e.g., number of seats),configuration of the trunk and engine compartments, etc. Additionally itshould be understood that in some vehicles multiple battery packs may beused. The use of a multiple pack design may be due to the use ofmultiple drive motors, or simply as a means of achieving the desiredweight distribution.

Given that a typical mounting location for a vehicle's battery pack isunderneath the car, and often at least partially under or behind thepassenger compartment, management of the flow of hot gas and smoke aswell as the containment of thermal energy released during a propagatingthermal runaway event is critical to the safety of the passengers. Asthe contents of a battery pack undergoing thermal runaway may reachtemperatures of 850° C. or greater, one aspect of the present inventionis to minimize the amount of thermal energy passing directly into thepassenger compartment from the battery pack, for example along pathway103 in the exemplary configuration shown in FIGS. 1 and 2. Additionally,as a large amount of smoke is generated during such a thermal event dueto the combustion of various battery and battery pack materials, anothergoal of the present invention is to direct the flow of hot gas and smokeaway from the egress points, thus insuring that the vehicle's passengerscan safely exit the car.

FIG. 3 is a perspective view of a preferred embodiment of a battery packenclosure 101 fabricated in accordance with the invention. Many featuresof this enclosure are described in detail in co-pending U.S. patentapplication Ser. No. 12/386,684, filed Apr. 22, 2009, the disclosure ofwhich is incorporated herein by reference for any and all purposes. Itwill be appreciated that the size and shape of the enclosure are basedon the design criteria of the vehicle and that enclosure 101 is meant tosimply illustrate the invention, not limit its application.

As shown in FIG. 3, a plurality of individual batteries 303 are mountedwithin a multi-piece enclosure that is designed to withstand the hightemperatures associated with a propagating thermal runaway event. Assuch, enclosure 101 is preferably fabricated from steel or a similarmetal that has a melting point of greater than 800° C., more preferablygreater than 1000° C., and still more preferably greater than 1200° C.Alternately, enclosure 101 may be fabricated from a lower melting pointmaterial, i.e., a material with a melting point less than 800° C., butwith an inner liner comprised of a material that prevents the outerenclosure wall from melting during the thermal runaway event. Forexample, enclosure 101 may be comprised of an outer layer of aluminum,and coated on the enclosure's interior surface with a thermal insulator(e.g., a ceramic such as a carbide, nitride or silicide, or anintumescent material) that prevents the temperature of the outer layerfrom exceeding its melting point.

Enclosure 101 is comprised of a lower housing member 305 and a lid orupper housing member 307. As the invention is not limited to a specificbattery chemistry, geometry, specific number of cells or batteryinterconnect configuration, further details regarding such are notprovided herein.

As noted above, during a thermal runaway event hot gas is expelled bythe cells undergoing thermal runaway. Accordingly, it is important thatenclosure 101 not allow the hot gas to escape the enclosure, except inthe preconfigured region or regions as described below (i.e., thefailure points designed into the enclosure). Therefore the walls of theenclosure are preferably welded together, assuming the enclosure wallsare fabricated from a weldable material. Other fabrication means mayalso be used, such as riveting, as long as the enclosure is able tomaintain its shape during a thermal event and does not permit hot gasand/or flammable material to escape the enclosure along an undesiredpath (e.g., into the passenger compartment). It will be appreciated thatthe wall thickness for the enclosure is determined on the basis of theselected material, the dimensions of the enclosure, and the size andweight of the cells to be housed within the enclosure.

In order to prevent the escape of hot gas and/or flammable material inundesired locations, preferably a compressible seal 309 is interposedbetween the complimentary and mating surfaces of lower housing member305 and upper housing member 307. Seal 309 may be fabricated from avariety of different materials, although metal sealing gaskets arepreferred due to the high temperatures encountered during a thermalevent.

Preferably lower housing member 305 includes a flange 311 onto which thesealing gasket, if used, is positioned. In the illustrated embodiment,upper housing member 307 is flat, however, in embodiments in which anon-flat upper housing member is used, the upper housing memberpreferably also includes a flange that is complimentary to flange 311.Enclosure 101 includes means, for example a plurality of bolts 313, forcompressing seal 309 and holding together the housing members. Bolts 313may also be used to attach enclosure 101 to the mounting structure ormounting bay of the electric or hybrid vehicle.

It will be appreciated that enclosure 101 requires the inclusion ofvarious couplings that pass through one or more walls of the enclosure.For example, the enclosure requires a plurality of electrical connectors315 that allow connection to be made to the cells within the pack.Electrical connectors are also required for coupling to any sensorsmaintained within the enclosure, for example temperature sensors.Additionally, assuming the use of an active battery cooling system, theenclosure may also include coolant line connectors 317.

During a propagating thermal event, due to the high temperature and theincreased pressure, enclosure connectors are prone to failure. Failure,in this sense, does not refer to the connectors no longer functioning asintended, i.e., no longer passing electrical power from the battery pack(i.e., connectors 315) or coolant for the battery cooling system (i.e.,connectors 317). Rather, failure in this sense refers to the connectorsproviding a path for hot gas and flammable materials to pass out of thebattery pack enclosure. In at least one embodiment of the invention,connector failure is intended and the connectors are located to insurethat the hot gas and material are exhausted out of the enclosure in thedesired locations as described further below. Alternately, theconnectors can be designed to withstand the temperature and pressure ofa propagating thermal runaway event. In this embodiment, preferablyelectrical connectors 315 utilize a combination of a high temperatureceramic as the insulator, and a high melting point metal for theconductors. In this same embodiment, preferably metal coolant connectors317 are used, along with metal coolant lines, thus preventing theconnectors from becoming unintended enclosure failure points during athermal event.

Pressure differentials between the inner volume of the enclosure and theoutside environment may be caused by the battery pack being moved to adifferent altitude, and thus subjected to a different external pressure.Pressure differentials can also arise due to component out-gassing,battery cell venting, temperature changes, etc. As enclosure 101 isdesigned to contain a propagating thermal runaway event, and to directgenerated hot gas and flammable materials through pre-configured failurepoints, it has sufficient structural strength and rigidity to tolerateordinary pressure differentials. Alternately, in at least oneembodiment, a pressure management system is used to ensure that thepressure differential between the inner volume of the enclosure and theoutside environment stays within a predetermined range during normalbattery pack operation. Preferably the pressure management system iscomprised of one or more pressure relief valves 319 coupled to enclosure101. Preferably pressure relief valve or valves 319 are two-way valves.If the enclosure utilizes pressure a relief valve, preferably thepressure relief valve or valves are used not only as a means ofmaintaining the pressure within the enclosure within the desiredoperating range during normal battery pack operation, but also asenclosure failure points that are intended to allow hot gas to exit theenclosure during a thermal runaway event. In such an embodiment, eitherthe pressure relief valves are designed to allow sufficient gas to passthrough during a thermal runaway event to prevent catastrophicover-pressurization of the enclosure, or other enclosure failuremechanisms are incorporated into the enclosure as described below inaddition to the pressure relief valve(s).

As previously noted, the enclosure of the present invention is designedto control and direct the flow of hot gas and flammable materials duringa propagating thermal runaway event using one or more enclosure failureports 321, the enclosure failure port(s) preferably directing the flowof hot gas and flammable materials away from the passenger compartmentas well as the passenger compartment egress points (e.g., doors,windows). FIG. 4 illustrates one type of enclosure failure port. In thisembodiment, a portion 401 of enclosure sealing gasket 403 is designed tofail when the temperature and/or pressure exceeds the normal operatingrange of the battery enclosure, thus providing a port for exhausting hotgas from the enclosure. In this embodiment preferably the enclosure sealis comprised of multiple sections, e.g., sections 401 and 403 wheresection 401 is comprised of a material with a lower melting point thanthat of section 403. Note that region 401 of the enclosure gasket may bedesigned to mate to a channel as described relative to FIG. 17, thusallowing the flow of hot gas to be directed as desired. FIGS. 5 and 6illustrate another type of enclosure failure port. In these figures, aportion 501 of a wall of enclosure 101 is shown. As illustrated, a cover503 is sealed to enclosure wall 501 with a sealant 601, cover 503covering a hole 603 within the enclosure wall. Cover 503 may befabricated from the same material as the enclosure, or from a differentmaterial. Sealant 601 may be comprised of a bonding material, solder oranother type of fastener. Seal 601 is selected to provide an adequatestructural seal during normal battery pack usage, but to fail whensubjected to a predetermined and abnormal temperature (e.g., greaterthan 250° C.; greater than 500° C.; etc.) and/or a predetermined andabnormal pressure (e.g., greater than 5 psi; greater than 10 psi; etc.).When seal 601 fails, cover 503 blows away from the enclosure wall, thusallowing the enclosure to vent the hot gas and flammable materials. FIG.7 illustrates an alternate type of enclosure failure port. As shown inthe cross-sectional view of FIG. 7, in this exemplary configurationenclosure wall 501 is sufficiently thinned at a region 701 that it willfail as the temperature and the pressure within the enclosure increasesduring the thermal event. FIG. 8 illustrates an alternate type ofenclosure failure port. As shown in the cross-sectional view of FIG. 8,in this exemplary configuration a portion 801 of enclosure wall 501 issurrounded by scoring 803, thereby allowing portion 801 to fail alongscoring 803 as the temperature and the pressure within the enclosureincreases during the thermal event. FIGS. 9 and 10 illustrate analternate enclosure failure port in which a cover 901, fabricated from arelatively low melting point material, is bonded, soldered, welded orotherwise fastened to enclosure wall 501, cover 901 covering hole 603(also referred to herein as a port). Cover 901 may be fabricated fromany of a variety of different materials that will melt, thereby openingport 603, when the temperature exceeds a predetermined temperature(e.g., greater than 250° C.; greater than 500° C.; etc.) and/or apredetermined pressure (e.g., greater than 5 psi; greater than 10 psi;etc.). Exemplary materials include metals and alloys, e.g., aluminumwith a melting temperature of 659° C., and plastics, composites, etc. Inthe illustrated embodiment, cover 901 is attached to wall 501 at joint1001. Note that this embodiment is similar to that shown in FIGS. 5 and6, except that during a thermal runaway event, the cover fails asopposed to the cover seal. FIGS. 11 and 12 illustrate an alternateembodiment in which cover 1101 is held in place against enclosure wall501 using a plurality of bolting members 1103 (e.g., bolts, rivets,etc.). In this embodiment, bolts/rivets 1103 are designed to fail as thetemperature and pressure within enclosure 101 increase beyond normal.

The enclosure failure mechanisms described above are designed to failcompletely during a major thermal runaway event. In a minor variation,the enclosure failure port is designed to guide the flow of hot gas andmaterial exiting the enclosure during such an event. In general, themechanisms described above may be used, except that the cover is heldmore firmly in one area than the remaining area. For example, theembodiment shown in FIGS. 5 and 6 may be modified as shown in FIGS. 13and 14. In this configuration, two different materials are used for theseal, a first material 1301 along most of the cover/wall junction, and asecond material 1303 along a small portion of the cover/wall junction.By using a material for seal 1303 with a higher melting point than thatof material 1301, when the temperature and pressure within enclosure 101gets high enough, seal 1301 gives away before seal 1303. As a result,hot gas and flammable material is directed along path 1401 as shown.Clearly the other enclosure failure systems may also be modified toachieve directed gas flow out of the enclosure upon failure. Forexample, the embodiment shown in FIG. 7 may be modified by increasingthe thickness in a portion 1501 of the perimeter of cover 1503 relativeto the remaining portion 1505 (FIGS. 15 and 16). When the temperatureand pressure increases sufficiently, region 1505 breaks or melts first,allowing cover 1503 to bend along perimeter portion 1501. Similarly, thescoring 803 of the embodiment shown in FIG. 8 may have a variable depth,thereby allowing region 801 to open in a predetermined manner. Theembodiment illustrated in FIGS. 9 and 10 may be modified by varying thethickness of cover 901 so that as the cover begins to melt, itpreferentially melts, thereby creating a path for directing the escapinghot gas. The embodiment illustrated in FIGS. 11 and 12 may be modifiedby using bolts or rivets with different melting points, thus allowingthe cover to break-away from enclosure 101 in a predictable fashion.

In accordance with the invention, the region of intended enclosurefailure is located such that the hot gas and materials expelled from theenclosure are directed away from the passenger compartment, andpreferably away from any location that might interfere with passengersleaving the vehicle or emergency aid coming to the assistance of thepassengers. Additionally, it is preferred that the flow of hot gas andmaterial be directed away from flammable materials, thus reducing therisk of the thermal runaway event leading to additional vehicle, orother, damage. An example of preferred flow directions is given in FIG.1 in which hot gas and material is preferably exhausted from theenclosure in a direction 105 that directs the flow downwards towards thepavement under the car, or in a direction that directs the flow awayfrom the vehicle, e.g., direction 107 that directs the flow downwardsand backwards towards the pavement and the rear of the vehicle. Notethat as the vehicle will likely be stopped during this process, analternate preferred flow direction is downwards and forwards towards thepavement and the front of the vehicle. It will be appreciated that thedesired flow direction depends upon the location of the battery packenclosure relative to the passenger compartment, and the design of thepassenger compartment itself. For example, if the battery pack enclosureis mounted under the car, and at the very rear of the car, one preferredflow direction would be towards the rear of the car, away from thepassenger compartment and the vehicle itself. As used herein, and asnoted above, enclosure connectors (e.g., electrical or coolantconnectors), pressure relief valves, or dedicated failure mechanisms(e.g., as illustrated in the exemplary embodiments of FIGS. 4-16) mayall be used to provide the desired battery pack enclosure failureport(s). Note that these enclosure failure ports may be designed to failbased only the internal pressure of the enclosure (i.e., over-pressure),based only on the internal temperature of the enclosure (i.e.,over-temperature), or based on a combination of both as is preferred.

In at least one embodiment, in addition to providing enclosure failureports, the ports are coupled to heat resistant channels that allowfurther direction of the flow of hot gas and material away from thepassenger compartment regardless of the mounting location of the batterypack. By directing the flow of hot gas further from the passengercompartment, the likelihood of harming passengers or initiating vehiclefires is reduced. Additionally, by directing the flow of smoke, burningdebris, etc. far away from the passenger compartment, passengervisibility is increased, as is passenger access to fresh air. FIG. 17illustrates this aspect of the invention. As shown, a pair of heatresistant ducts 1701/1703 direct the flow of hot gas/debris from a pairof enclosure failure ports 1705/1707, respectively. It will beappreciated that this is simply an exemplary configuration, and that theinvention may utilize a fewer or greater number of channels, and thechannels may couple to the enclosure at different locations, and thechannels may direct the flow in different directions than shown.

The heat resistant channels of this embodiment, e.g., channels 1701 and1703, may either utilize an open design as illustrated by thecross-sectional view of channel 1801 in FIG. 18, or a closed design asillustrated by the cross-sectional view of channel 1901 in FIG. 19. Ifan open channel design is used, the open portion of the channel isoriented relative to the vehicle to direct the flow of hot gas andmaterial away from the vehicle. Note that the heat resistant channelsmay be fabricated from any of a variety of materials that are intendedfor high temperature applications. For example, in one embodiment ametal conduit is used, for example a steel conduit. In anotherembodiment, a metal conduit is used with an outer or an inner hightemperature insulator. In yet another embodiment, the heat resistantchannel is comprised of inner and outer metal conduits with a thermallyinsulating material interposed between the two conduit layers.

In at least one embodiment, in addition to configuring the battery packenclosure with one or more enclosure failure ports that direct the flowof hot gas and flammable material away from the passenger compartment,one or more thermal insulators are located between the battery packenclosure 101 and the passenger compartment. The purpose of the thermalinsulation surrounding some, or all, of the battery pack enclosure is toreduce the flow of heat from enclosure 101 to the passenger compartment,thereby further protecting the passengers from harm. Additionally, in atleast one embodiment thermal insulation is also interposed between thebattery pack enclosure and any flammable materials located in proximityto the battery pack, thus reducing the risk of vehicle fires.

FIG. 20 illustrates an exemplary configuration in which only thoseportions of the battery pack enclosure 101 adjacent to the passengercompartment and/or adjacent to flammable materials are thermallyinsulated with thermal insulator 2001, thus allowing other enclosuresurfaces such as surface 2003 to radiate heat, thereby aiding enclosurecooling. The material selected for thermal insulator 2001 as well as theselected thickness and location for this layer or layers depends on thenumber and type of cells within the battery pack as the expectedtemperature and duration of a propagating thermal runaway event dependson these factors. Additionally, the material and thickness of thethermal insulation depends on the mounting location of the battery packand the proximity of the battery pack to the passenger compartmentand/or flammable materials. In general, the maximum projectedtemperature of the exterior surface of the battery pack enclosure iscalculated as well as the expected duration of a propagating thermalrunaway event. For the thermal insulation interposed between thepassenger compartment and the battery pack enclosure, this informationis used along with the thermal design goals for the passengercompartment to calculate the requirements for the thermal insulation.Typically, the passenger compartment goals are given in terms of themaximum temperature allowed within the passenger compartment for thefirst ‘x’ number of minutes after the onset of a thermal event. Thesegoals are intended to insure that passengers will be given sufficienttime after a thermal event begins to safely exit the vehicle or foremergency responders to extract the passengers from the vehicle. For thethermal insulation interposed between the battery pack enclosure andflammable materials, the design goal of a preferred embodiment is toprevent the heat generated during a thermal event from initiatingsecondary fires of vehicle flammable materials or increasing thetemperature within the passenger compartment beyond tenable levelsbefore a predetermined length of time.

After determining the desired thermal insulation properties based bothon the expected characteristics of a battery pack thermal event for theintended battery pack and on the design criteria imposed by the thermaldesign goals for the passenger compartment and adjacent flammablematerials, then specific thermal insulators are selected. In addition tothe thermal properties of the insulation, cost, ease of manufacturing,and insulation weight are also considered in selected the thermalinsulator(s). It will be appreciated that there are a wide range ofacceptable thermal insulators, depending upon the design goals for thematerial that are driven, in large part and as noted above, on the exactconfiguration of the battery pack, battery pack enclosure, vehicle, andenclosure mounting. In addition to thermal insulators (e.g., fiberglass;silica, titania, carbon and/or alumina based materials, etc.), it isexpected that any of a variety of fire retardant materials (e.g.,intumescent materials, etc.) may also be used, either as a replacementfor the thermal insulation, or as an additional layer used inconjunction with the thermal insulator. The location and profile of thefire retardant materials may be the same as the thermal insulators ormay be in select areas (e.g., only near the designed failure port).

In at least one embodiment, and as illustrated in FIG. 21, a fan(s) 2101is used to reduce the flow of thermal energy from enclosure 101 to thepassenger compartment and/or regions of flammable material by directinga flow of fresh air between the enclosure and adjacent vehicle regions(e.g., passenger compartment). In one embodiment, fan 2101 has an airintake forward of the battery pack enclosure. As a result, during normalbattery pack and vehicle operation and while the car is moving forward,fresh air may be being forced past the enclosure, thus drawing off heatand cooling the battery pack enclosure while simultaneously reducing theflow of heat to adjacent vehicle regions. The air from the fan/fanintake may simply be routed through a region between the passengercompartment and the battery pack, or directed through one or more heatresistant channels 2103 before being directed away from the vehicle andthe passenger compartment. Preferably one or more temperature sensors2105 detect when the battery pack enclosure temperature is above thedesired operating range. Typically temperature sensors 2105 are the samesensors used to monitor battery temperature and detect the onset ofthermal runaway. Once sensors 2105 detect an elevated temperature,indicating the onset of thermal runaway, an appropriate signal is sentto fan controller 2107 to initiate fan operation.

As will be understood by those familiar with the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. Accordingly, thedisclosures and descriptions herein are intended to be illustrative, butnot limiting, of the scope of the invention which is set forth in thefollowing claims.

1. A battery pack thermal management system, comprising: a battery packenclosure configured to hold a plurality of batteries, wherein saidbattery pack enclosure is comprised of a high temperature material; andan enclosure failure port assembly integrated into a wall of saidbattery pack enclosure, wherein said wall of said battery pack enclosurehas a first wall thickness, wherein said enclosure failure port assemblyremains closed during normal operation of said battery pack, and whereinsaid enclosure failure port assembly opens during a battery pack thermalrunaway event and provides a flow path for exhausting hot gas fromwithin said battery pack enclosure, wherein said enclosure failure portassembly directs said flow path at an angle away from a normal of saidwall of said battery pack enclosure, and wherein said enclosure failureport assembly further comprises: a substantially circular region of saidwall, said substantially circular region having a second wall thicknessthat is thinner than said first wall thickness; a transition regioninterposed between said substantially circular region and a surroundingportion of said wall that surrounds said substantially circular region,wherein a first portion of said transition region encircling a firstportion of said substantially circular region has a third wall thicknessthat is thicker than said second wall thickness and thinner than saidfirst wall thickness, wherein a second portion of said transition regionencircling a second portion of said substantially circular region has afourth wall thickness that is thinner than said second wall thicknessand thinner than said first wall thickness, wherein said second portionof said transition region fails before said first portion of saidtransition region during said battery pack thermal runaway event andallows hot gas from within said battery pack enclosure to exhaustthrough said substantially circular region at an angle away from saidnormal of said wall of said battery pack enclosure.
 2. The battery packthermal management system of claim 1, wherein said high temperaturematerial is comprised of a metal with a melting temperature greater than800° C.
 3. The battery pack thermal management system of claim 1,wherein said high temperature material is comprised of a metal with amelting temperature greater than 1000° C.
 4. The battery pack thermalmanagement system of claim 1, wherein said high temperature material iscomprised of at least an outer layer and an inner layer, wherein saidinner layer is comprised of a ceramic.
 5. The battery pack thermalmanagement system of claim 4, wherein said ceramic inner layer preventssaid outer layer from melting during said battery pack thermal runawayevent.
 6. The battery pack thermal management system of claim 1, whereinsaid high temperature material is comprised of at least an outer layerand an inner layer, wherein said inner layer is comprised of anintumescent material.
 7. The battery pack thermal management system ofclaim 6, wherein said intumescent material inner layer prevents saidouter layer from melting during said battery pack thermal runaway event.8. The battery pack thermal management system of claim 1, wherein saidbattery pack enclosure further comprises: a first housing memberconfigured to hold said plurality of batteries; a second housing memberconfigured to be coupled to said first housing member; and means tosecure said first housing member to said second housing member.
 9. Thebattery pack thermal management system of claim 8, wherein said batterypack enclosure further comprises a sealing gasket configured to fitbetween a first sealing surface corresponding to said first housingmember and a second sealing surface corresponding to said second housingmember, said sealing gasket further configured to be interposed betweensaid first and second sealing surfaces when said first housing member issecured to said second housing member.
 10. The battery pack thermalmanagement system of claim 1, wherein said enclosure failure portassembly opens when an internal battery pack temperature exceeds apreset temperature.
 11. The battery pack thermal management system ofclaim 1, wherein said enclosure failure port assembly opens when aninternal battery pack temperature exceeds a preset temperature and aninternal battery pack pressure exceed a preset pressure.
 12. The batterypack thermal management system of claim 1, further comprising a heatresistant channel, wherein an entrance of said heat resistant channel isproximate to said enclosure failure port assembly, and wherein duringsaid battery pack thermal runaway event hot gas is exhausted out of saidenclosure failure port assembly and into said entrance of said heatresistant channel.
 13. The battery pack thermal management system ofclaim 12, wherein said battery pack enclosure is mounted to a vehicle,wherein said hot gas exhausted through said enclosure failure portduring said thermal runaway event passes through said heat resistantchannel, and wherein an exit port of said heat resistant channel directssaid hot gas away from a vehicle passenger compartment.
 14. The batterypack thermal management system of claim 12, wherein said heat resistantchannel utilizes an open channel design.
 15. The battery pack thermalmanagement system of claim 12, wherein said heat resistant channelutilizes a closed channel design.
 16. The battery pack thermalmanagement system of claim 1, wherein said battery pack enclosure ismounted to a vehicle, wherein said battery pack thermal managementsystem further comprises at least one layer of a thermal insulatorpositioned between said battery pack enclosure and a vehicle passengercompartment.
 17. The battery pack thermal management system of claim 1,wherein said battery pack enclosure is mounted to a vehicle, whereinsaid battery pack thermal management system further comprises at leastone layer of a fire retardant material positioned between said batterypack enclosure and a vehicle passenger compartment.
 18. The battery packthermal management system of claim 17, wherein said fire retardantmaterial is comprised of an intumescent material.